Smoke sensors using the optical scatter principal are increasingly becoming the most common type of fire sensor on the market. Optical sensors however are very sensitive to non-fire aerosols like water vapor (condensed steam and mist), dust and ash, spores, cooking aerosols, insects and spiders.
Optical techniques are becoming common that attempt to differentiate between different types of smoke and non-smoke aerosols. Common techniques used in an optical scatter chamber are the use of different wavelength LEDS e.g. blue and near infra-red or different scatter angles e.g. 140 degrees and 70 degrees (or even a combination of both). In all these techniques a ratio is made between two different optical scatter paths in a common chamber. This ratio can then indicate the particle size of the aerosol in the chamber and therefore if the smoke is grey (larger particles) or black (smaller particles). That can be very difficult, is detecting non-fire aerosols, for example water vapor, as this can be generated at extremely high levels over a range of particle sizes very similar to the particle size of grey smoke. Therefore depending on the conditions under which the water vapor is generated, little or no difference can be detected in the optical ratio from that of grey smoke.
Note that this can also be true of other non-fire aerosols, so much so that manufactures usually resort to reducing false alarms by making the smoke sensor have a low sensitivity to grey smoke and by the use of spike detection (delaying detection if the aerosol profile changes too fast). It should be noted that repeated spike detection may also produce an excessive smoke detection delay. An alternative technique is to use a very fine filter material on the sensor and suck air thought it into the smoke chamber. Using such fine filters will require regular maintenance well before it starts to block the detection of larger smoke particles.